1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which have the electrophotographic photosensitive member.
2. Description of the Related Art
Electrophotographic photosensitive members used in electrophotographic apparatus such as copying machines and laser beam printers are required to have a sufficient sensitivity to imagewise exposure light, and the development of techniques for improving in sensitivity of electrophotographic photosensitive members has been being put forward. Techniques for improving in sensitivity of electrophotographic photosensitive members by using highly sensitive charge generating materials such as azo pigments and phthalocyanine pigments in photosensitive layers of electrophotographic photosensitive members are disclosed in Japanese Patent Applications Laid-open No. S59-31962, No. H01-183663, No. H10-67946 and No. H09-34149.
However, with such improvement in sensitivity of electrophotographic photosensitive members, electric charges (photocarriers) formed more tend to remain in the photosensitive layer to tend to cause variations in potential as a sort of memory.
Stated specifically, light-area potential and residual potential tend to come to decrease at the time of continuous printing. For example, where an electrophotographic photosensitive member is used in a development process in which the part of dark-area potential is made to serve as non-development part and the part of light-area potential as development part (what is called a reversal-development system), the areas to which the imagewise exposure light has been applied at the time of earlier printing come good in sensitivity. Hence, what is called positive ghost may unwantedly appear, which is a phenomenon that the part exposed to imagewise exposure light at the time of earlier printing appears indistinctly in black when a whole-area white image is reproduced at the time of next printing. Conversely, the light-area potential tends to come to increase at the initial stage of printing. For example, where the electrophotographic photosensitive member is used in the reversal-development system, the areas to which the imagewise exposure light has been applied at the time of earlier printing come poor in sensitivity. Hence, what is called negative ghost may unwantedly appear, which is a phenomenon that the part exposed to imagewise exposure light at the time of earlier printing appears indistinctly in white when a whole-area black image is reproduced at the time of next printing.
In particular, where an intermediate layer having a barrier function and so forth is provided between a support and a photosensitive layer, the intermediate layer has so high volume resistivity in a low-temperature and low-humidity environment that the electric charges may tend to remain in the photosensitive layer to tend to make the ghost phenomenon occur conspicuously.